The present invention relates to an article and method for fire protecting a duct. More specifically, the present invention relates to an article for fire protecting a fire-rated duct, where the article contains an intumescent material, and has an initial thickness of less than about three inches when in a first application condition and an expanded thickness when in a second heated condition, where the expanded thickness is greater than the initial thickness.
Fire-rated ducts are found in many commercial, industrial, and residential applications, including kitchen grease ducts, chemical exhaust ducts, heating, ventilation, and air conditioning ducts, and any general purpose supply or exhaust ducts. A fire-rated duct may be wrapped with a fire-protecting, noncombustible material to create a fire-resistant barrier around the duct. If a fire begins inside the duct, the fire-resistant barrier helps to contain the fire within the duct, so that the fire does not spread to a structure surrounding the duct. The fire-protecting materials are commonly called “fire wraps”, “duct wraps”, “fire-protecting sheets”, “fire-protecting blankets”, or generally, “fire-protecting articles”.
Conventional fire-protecting articles for ducts utilize multiple layers of fibers, such as glass, mineral, or ceramic fibers, or blends thereof. With a conventional fire-protecting article, two layers of an approximately two-inch thick fire-protecting article are needed in order for the duct protection to pass the applicable fire tests. One of the most rigorous tests a fire-protecting article must pass is the AC101 Acceptance Criteria for Grease Duct Enclosure Assemblies, as specified by the International Council of Building Officials (ICBO, which is now a part of ICC Evaluation Service, Inc.) in April 2001. In Section 5.5 of the AC101 criteria, a sample of a fire-protecting article is exposed to a furnace that is exerting a heat of approximately 2000 degrees Fahrenheit (° F.) for about 30 minutes. The fire-protecting article sample must be able with stand the 2000° F. heat. That is, the fire-protecting article sample must not combust, and the temperature measured at an outermost portion of the fire-protecting article (the portion of the fire-protecting article furthest from the furnace) must not exceed 325° F. plus the ambient temperature. In Section 5.4 of the AC101 criteria, a sample of the fire-protecting article is exposed to a furnace that is exerting a heat of approximately 500° F. for about four hours. The temperature measured at an outermost portion of the fire-protecting article (the portion of the fire-protecting article furthest from the furnace, which is also known as the “cold side”) must not exceed 117° F. plus the ambient temperature. It has been found that with conventional fire-protecting articles, two layers of the fire-protecting article (for a total of approximately four inches of fire-protecting article) are needed in order for the temperature at the outermost portion of the fire-protecting article to remain at or below about 325° F. plus the ambient temperature in the Section 5.5 test and at or below about 117° F. in the Section 5.4 test.
The fire-protecting article is usually installed between the duct and the surrounding structure. Oftentimes, the space between the duct and surrounding structure is only large enough to fit the conventional fire-protecting article. Because of the tight working space, it may be difficult to install the conventional fire-protecting article. Furthermore, when two layers of the conventional fire-protecting article are used, the installation process may be burdensome.